1. Field
One embodiment of the invention relates to a digital broadcasting receiver which is capable of simultaneously displaying received images of a plurality of broadcasting programs on one display device, and recording any one of data on the received images.
2. Description of the Related Art
In recent years, a television receiver which simultaneously displays two television broadcastings in the form of a main picture and a sub picture on one display device has been put to practical use. This sort of television receiver has two tuners built therein in order to simultaneously display a main picture and a sub picture on one display device. In this case, one tuner is used for the main picture, and the other is used for the sub picture. For display of the main picture and the sub picture, there are display modes such as a picture-in-picture mode, a picture-by-picture mode, and a dual window mode in which two pictures are displayed on a left-hand side and a right-hand side of a screen of a display device, respectively. In addition, only one main picture can be displayed.
In a reception system using two tuners, a distributor distributes a signal received through one antenna into two signals, and the resulting two signals are inputted to the two tuners, respectively. However, the insertion of the distributor results in that antenna terminal voltages of the two tuners, that is, leakage voltages of a local oscillator interfere with each other, thereby degrading an image quality. In order to solve this problem, an amplifier for mutual isolation between the two tuners is provided between the distributor and the antenna. This technique, for example, is disclosed in the Japanese Patent Kokai No. 8-116497.
On the other hand, for start of a ground wave digital broadcasting, the development of a digital broadcasting receiver is in progress now. In the case of the digital broadcasting receiver, a noise factor (NF) from an antenna input to a digital modulation IC is dominant in reception sensitivity performance. Since an insertion loss (for example, 4 dB) of the distributor occurs when the distributor is inserted in the manner as has been described, the NF becomes worse, so that sensitivity of reception of a weak electric field becomes worse. Although the amplifier is provided in the preceding stage of the distributor in order to solve this problem, conversely, the amplifier generates a distortion due to input of a signal having a strong electric field, which results in the quality of received signal being degraded. In order to prevent this situation, the gain of the amplifier is set in consideration of a balance between the sensitivity for the weak electric field and the performance for the distortion caused by the strong electric field.
However, in the conventional digital broadcasting receiver, even when the gain of the amplifier is set in consideration of the balance between the sensitivity for the weak electric field and the performance for the distortion caused by the strong electric field, both the weak electric field and the strong electric field cannot be optimized in some cases. Therefore, it is difficult to receive the electric wave in the best state for any of the received signal having the weak electric field and the received signal having the strong electric field. In particular, in the digital broadcasting, there are the characteristics that when the received signal becomes weak in level, a bit error abruptly increases upon reduction of the received signal to a certain level. For this reason, the setting of the gain of the amplifier connected to the antenna is very important.